TR

tr (lower case) is a Unixcommand to replace or delete characters in a string of text. The most common use is:
tr "string1" "string2"
which copies the standard input to the standard output, replacing each character from "string1" with the corresponding character from "string2".
For example, this tr command will encode what you type as rot13:
tr 'a-zA-Z' 'n-za-mN-ZA-M'